With the earth's sources of copper diminishing rapidly, much emphasis has been placed on discovering new sources of this metal. One source of copper which has received much attention recently is manganese nodules which are found on the deep floors of oceans and lakes and which contain manganese, iron, copper, nickel, molybdenum, cobalt and other metal values.
Ocean floor deposits are found as nodules, loose-lying at the surface of the soft sea floor sediment, as grains in the sea floor sediments, as crusts on ocean floor hard rock outcrops, as replacement fillings in calcareous debris and animal remains, and in other less important forms. Samples of this ore material can readily be recovered on the ocean floor by drag dredging or by deep sea hydraulic dredging.
The character and chemical content of the deep sea nodules may vary widely depending upon the region from which the nodules are obtained. The Mineral Resources of the Sea, John L. Mero, Elsvier Oceanography Series, Elsevier Publishing Company, 1965, discusses on pages 127-241 various aspects of manganese nodules. For the purpose of illustrating this invention, the complex ores will be considered as containing the following approximate metal content range on a dry basis:
______________________________________ METAL CONTENT ANALYSIS RANGE ______________________________________ Copper 0.8-1.8% Nickel 1.0-2.0% Cobalt 0.1-0.5% Molybdenum 0.03-0.1% Manganese 10.0-40.0% Iron 4.0-25.0% ______________________________________
The remainder of the ore consists of oxygen as oxides, clay minerals with lesser amounts of quartz, apatite, biotite, sodium and potassium feldspars and water of hydration.
Prior to the present invention, of the many ingredients making up the manganese nodules, copper and nickel were emphasized and the manganese was not.
In general, the base metal values such as copper, nickel, cobalt and molybdenum are recovered from manganese nodules by reducing the nodules to break down the manganese oxide to enable the metal values contained therein to be leached in a leach liquor from which they are recovered. In practicing the present invention, the reduction may be performed by pyrometallurgical roasting operations or by a hydrometallurgical process known as the "cuprion" process which is disclosed in U.S. Pat. No. 3,938,017, the teachings of which are incorporated herein by reference. At this point, it should be noted that U.S. Pat. No. 3,938,017 does not disclose any method of treating the tailings which consist largely of manganese and iron even though manganese is a valuable metal which is employed in great quantities in making steel.
In U.S. patent application Ser. No. 927,272 entitled Production of Ferromanganese From Manganese Nodules, filed on even data herewith by Schapiro et al., a process is disclosed for concentrating manganese from nodule tailings. The present invention is an improvement on the process disclosed in that application.